Commit 0e04d4ce authored by David Howells's avatar David Howells
Browse files

FS-Cache: Add cache tag handling 



Implement two features of FS-Cache:

 (1) The ability to request and release cache tags - names by which a cache may
     be known to a netfs, and thus selected for use.

 (2) An internal function by which a cache is selected by consulting the netfs,
     if the netfs wishes to be consulted.

Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
Acked-by: default avatarSteve Dickson <steved@redhat.com>
Acked-by: default avatarTrond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
Tested-by: default avatarDaire Byrne <Daire.Byrne@framestore.com>
parent a6891645

fs/fscache/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -3,6 +3,7 @@ 
#



fscache-y := \

	cache.o \

	fsdef.o \

	main.o

fs/fscache/cache.c

0 → 100644
+166 −0
Original line number Diff line number Diff line 
/* FS-Cache cache handling

 *

 * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.

 * Written by David Howells (dhowells@redhat.com)

 *

 * This program is free software; you can redistribute it and/or

 * modify it under the terms of the GNU General Public License

 * as published by the Free Software Foundation; either version

 * 2 of the License, or (at your option) any later version.

 */



#define FSCACHE_DEBUG_LEVEL CACHE

#include <linux/module.h>

#include <linux/slab.h>

#include "internal.h"



LIST_HEAD(fscache_cache_list);

DECLARE_RWSEM(fscache_addremove_sem);



static LIST_HEAD(fscache_cache_tag_list);



/*

 * look up a cache tag

 */

struct fscache_cache_tag *__fscache_lookup_cache_tag(const char *name)

{

	struct fscache_cache_tag *tag, *xtag;



	/* firstly check for the existence of the tag under read lock */

	down_read(&fscache_addremove_sem);



	list_for_each_entry(tag, &fscache_cache_tag_list, link) {

		if (strcmp(tag->name, name) == 0) {

			atomic_inc(&tag->usage);

			up_read(&fscache_addremove_sem);

			return tag;

		}

	}



	up_read(&fscache_addremove_sem);



	/* the tag does not exist - create a candidate */

	xtag = kzalloc(sizeof(*xtag) + strlen(name) + 1, GFP_KERNEL);

	if (!xtag)

		/* return a dummy tag if out of memory */

		return ERR_PTR(-ENOMEM);



	atomic_set(&xtag->usage, 1);

	strcpy(xtag->name, name);



	/* write lock, search again and add if still not present */

	down_write(&fscache_addremove_sem);



	list_for_each_entry(tag, &fscache_cache_tag_list, link) {

		if (strcmp(tag->name, name) == 0) {

			atomic_inc(&tag->usage);

			up_write(&fscache_addremove_sem);

			kfree(xtag);

			return tag;

		}

	}



	list_add_tail(&xtag->link, &fscache_cache_tag_list);

	up_write(&fscache_addremove_sem);

	return xtag;

}



/*

 * release a reference to a cache tag

 */

void __fscache_release_cache_tag(struct fscache_cache_tag *tag)

{

	if (tag != ERR_PTR(-ENOMEM)) {

		down_write(&fscache_addremove_sem);



		if (atomic_dec_and_test(&tag->usage))

			list_del_init(&tag->link);

		else

			tag = NULL;



		up_write(&fscache_addremove_sem);



		kfree(tag);

	}

}



/*

 * select a cache in which to store an object

 * - the cache addremove semaphore must be at least read-locked by the caller

 * - the object will never be an index

 */

struct fscache_cache *fscache_select_cache_for_object(

	struct fscache_cookie *cookie)

{

	struct fscache_cache_tag *tag;

	struct fscache_object *object;

	struct fscache_cache *cache;



	_enter("");



	if (list_empty(&fscache_cache_list)) {

		_leave(" = NULL [no cache]");

		return NULL;

	}



	/* we check the parent to determine the cache to use */

	spin_lock(&cookie->lock);



	/* the first in the parent's backing list should be the preferred

	 * cache */

	if (!hlist_empty(&cookie->backing_objects)) {

		object = hlist_entry(cookie->backing_objects.first,

				     struct fscache_object, cookie_link);



		cache = object->cache;

		if (object->state >= FSCACHE_OBJECT_DYING ||

		    test_bit(FSCACHE_IOERROR, &cache->flags))

			cache = NULL;



		spin_unlock(&cookie->lock);

		_leave(" = %p [parent]", cache);

		return cache;

	}



	/* the parent is unbacked */

	if (cookie->def->type != FSCACHE_COOKIE_TYPE_INDEX) {

		/* cookie not an index and is unbacked */

		spin_unlock(&cookie->lock);

		_leave(" = NULL [cookie ub,ni]");

		return NULL;

	}



	spin_unlock(&cookie->lock);



	if (!cookie->def->select_cache)

		goto no_preference;



	/* ask the netfs for its preference */

	tag = cookie->def->select_cache(cookie->parent->netfs_data,

					cookie->netfs_data);

	if (!tag)

		goto no_preference;



	if (tag == ERR_PTR(-ENOMEM)) {

		_leave(" = NULL [nomem tag]");

		return NULL;

	}



	if (!tag->cache) {

		_leave(" = NULL [unbacked tag]");

		return NULL;

	}



	if (test_bit(FSCACHE_IOERROR, &tag->cache->flags))

		return NULL;



	_leave(" = %p [specific]", tag->cache);

	return tag->cache;



no_preference:

	/* netfs has no preference - just select first cache */

	cache = list_entry(fscache_cache_list.next,

			   struct fscache_cache, link);

	_leave(" = %p [first]", cache);

	return cache;

}

fs/fscache/internal.h

+20 −0
Original line number Diff line number Diff line
@@ -27,6 +27,15 @@ 
#define FSCACHE_MIN_THREADS	4

#define FSCACHE_MAX_THREADS	32



/*

 * fsc-cache.c

 */

extern struct list_head fscache_cache_list;

extern struct rw_semaphore fscache_addremove_sem;



extern struct fscache_cache *fscache_select_cache_for_object(

	struct fscache_cookie *);



/*

 * fsc-fsdef.c

 */
@@ -168,6 +177,17 @@ extern const struct file_operations fscache_stats_fops; 
#define fscache_stat(stat) do {} while (0)

#endif



/*

 * raise an event on an object

 * - if the event is not masked for that object, then the object is

 *   queued for attention by the thread pool.

 */

static inline void fscache_raise_event(struct fscache_object *object,

				       unsigned event)

{

	BUG();  // TODO

}



/*****************************************************************************/

/*

 * debug tracing

include/linux/fscache.h

+8 −1
Original line number Diff line number Diff line
@@ -173,6 +173,8 @@ struct fscache_netfs { 
 * - these are undefined symbols when FS-Cache is not configured and the

 *   optimiser takes care of not using them

 */

extern struct fscache_cache_tag *__fscache_lookup_cache_tag(const char *);

extern void __fscache_release_cache_tag(struct fscache_cache_tag *);



/**

 * fscache_register_netfs - Register a filesystem as desiring caching services
@@ -218,6 +220,9 @@ void fscache_unregister_netfs(struct fscache_netfs *netfs) 
static inline

struct fscache_cache_tag *fscache_lookup_cache_tag(const char *name)

{

	if (fscache_available())

		return __fscache_lookup_cache_tag(name);

	else

		return NULL;

}
@@ -233,6 +238,8 @@ struct fscache_cache_tag *fscache_lookup_cache_tag(const char *name) 
static inline

void fscache_release_cache_tag(struct fscache_cache_tag *tag)

{

	if (fscache_available())

		__fscache_release_cache_tag(tag);

}



/**

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